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SubjectRe: Uartlite - ulite_transmit
Hi Peter,

> Hi,
>
> >> The problem is the uart_flush_buffer() call we see after uart_open() in
> >> 4. If doesn't seem to come from serial_core (only called from uart_close
> >> / uart_hangup), so presumably it comes from the TTY core or
> >> userspace. Could you add a bit more debug to figure out where exactly it
> >> comes from?
>
> Michal> Last week I have also implemented simple ioctl function for
> Michal> uartlite - just printk to see what happen. Look at the second
> Michal> log below.
>
> Michal> uart_open(0) called
> Michal> ulite_ioctl 5401 bff76a18
> Michal> n_tty_ioctl
> Michal> ulite_ioctl 540b 2
> Michal> n_tty_ioctl
> Michal> n_tty_ioctl_helper TCFLSH
> Michal> tty_perform_flush TCIOFLUSH
> Michal> tty_perform_flush TCOFLUSH
> Michal> tty_driver_flush_buffer
> Michal> uart_flush_buffer(0) called
>
> So your userspace is calling tcflush, and serial_core responds by
> flushing (dropping) the buffer. That seems like expected behaviour to
> me.
>
> This is presumably from the busybox getty applet, which does:
>
> static void termios_init(struct termios *tp, int speed, struct options *op)
> {
> speed_t ispeed, ospeed;
> /*
> * Initial termios settings: 8-bit characters, raw-mode, blocking i/o.
> * Special characters are set after we have read the login name; all
> * reads will be done in raw mode anyway. Errors will be dealt with
> * later on.
> */
> /* flush input and output queues, important for modems! */
> tcflush(0, TCIOFLUSH);
>
> You could change that to a tcdrain() if that's not what you want.
>

Great that's work. Just for the record it is tcdrain(STDOUT_FILENO);
Patch against busybox 1.14.3 version is below. Maybe worth to added it
mainline busybox.

Thanks for your big help.
Michal


diff --git
a/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c
b/software/petalinux-dist/user/busybox/busybo
index 24a182f..4c99e92 100644
--- a/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c
+++ b/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c
@@ -279,6 +279,8 @@ static void termios_init(struct termios *tp, int
speed, struct options *op)
* later on.
*/
#ifdef __linux__
+ /* wait until all output written to the stdout has been
transmitted */
+ tcdrain(STDOUT_FILENO);
/* flush input and output queues, important for modems! */
ioctl(0, TCFLSH, TCIOFLUSH); /* tcflush(0, TCIOFLUSH)? - same */
#endif

--
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian


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